#define  _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main() {
    float num = 0;
    float a = 1;
    for (int i = 1; i < 100; i++) {
        if (i % 2 == 0) {
            num = (1 / a) - (1 / (a + 1));
            a++;
        }
        else {
            num = (1 / a) + (1 / (a + 1));
            a++;
        }
    }
    printf("%f ", num);
    return 0;
}